Igniter safe and arm



IGNITER SAFE AND ARM Filed Jan. 5, 1567 INVENTORS. 405/967/5 50X@ BY734,600 5406+/ United States Patent 3,439,617 IGNITER SAFE AND ARMAubrey B. Boyd, Littleton, Colo., and Jarod L. Baugh, Loveland, Ohio,assignors to North American Rockwell Corporation, a corporation ofDelaware Filed Jan. 5, 1967, Ser. No. 607,559 Int. Cl. F42c 15/00 U.S.Cl. M12- 70.2 3 Claims ABSTRACT 0F THE DISCLOSURE A safe and arm devicefor solid propellant igniters having a housing in which is disposedshock detonating material. Fuses leading to the igniter are xedly heldin the housing adjacent the detonating material with a perforated rotordisposed between the fuses and the detonating material.

This invention relates to a safe and arm device. More particularly, theinvention relates to a device for utilization with an igniter for solidpropellant motors which is used as a safe and arm.

The present invention, relating to an igniter safe and arm, hasparticular use for the type of igniter disclosed in copendingapplication Ser. No. 469,973 filed June 30, 1965, now abandoned. In thecopending application, an igniter is disclosed formed of a mesh screenhaving attached thereto and wrapped about strands of explosive fusematerial such as Pyrocore. The screen is then coated with a combustiblemixture. Upon ignition of the Pyrocore, the combustible material andscreen were ignited causing virtually instantaneous combustion of theentire igniter. The initial ignition of the igniter transpires from theigniting of the Pyrocore leads which extend from the igniter body. Aswith most igniters, it is imperative that the Pyrocore be prevented fromaccidental ignition prior to the desired set time. Thus, a safe and armdevice is mandatory for the successful operation of the igniter.

Previous proposed concepts for safe and arm devices for remote ignitionfor the type of igniter described utilized devices where the charge forigniting the fuse material was in a rotor and thus subjected to rotarymovement from a safe to an arm position. The mechanical arrangement ofthe previous devices has been quite complex and such devices have notbeen easily adaptable for placement outside of the motor case. Anotherdisadvantage of prior art devices is that normally the electricaldetonator is disposed in a line with the fuse, thus extending the axiallength of the device.

Thus, it is an object of this invention to provide a simple safe and armdevice for ignition of solid propellant igniters.

Another object of this invention is to provide a safe and arm devicehaving a minimum of Working parts.

Still another object of this invention is to provide a safe and armigniter device wherein no additional boost charge is present in therotor.

The above and other objects of the invention will become apparent in thefollowing description.

The device of this invention comprises an outer shell housing electricaldetonators. Mounted on the shell is an electrical conductor forconducting current to the detonators within the shell. Means areprovided in the shell or housing for permanently afxing the ends of thefuses which lead to the igniter. The ends of the fuses are affixed toshock sensitive detonating material and are circumferentally disposedadjacent the radially oriented electrical detonators. Disposed betweenthe ends of the fuses and the electrical detonators is a rotor elementhaving apertures there/ln corresponding to the number of fuses. In asafe position, the rotor is disposed so as to block passage of ICC shookenergy from the electrical detonators if prematurely set off to the endsof the fuses. In an arm position, the rotor is rotated so as to alignthe apertures with the end of the fuses and electrical detonators suchthat when detonations occurs in the electrical detonator, the shockforce will pass through the aperture to the fuses. Itis believed theinvention will be better understood with regard to the followingdetailed description in which:

The figure is a cross-sectional View of the safe and arm device of theinvention.

Referring to the figure, there is shown a safe and arm device 11 of thisinvention mounted on a forward case head 13 of a solid rocket motor.'Such a location outside of the forward case head is a usual locationfor safe and arm devices in that it provides easy access for the armingof the motor, and is normally the shortest distance between the safe andarm device and the igniter which is normally disposed at the front endof the solid propellant grain. In this particular example, twopyrotechnic fuses 15 are shown which lead from the safe and arm deviceto the igniter for the solid propellant motor. Through-hole bodies 17are integrally welded at their bases 19 to the motor case head andextend forwardly therefrom. Through the center 18 of these bodies 17pass the fuses 15. The pyrotechnic fuse 15 has an insulation material 21about the center fuse element 23. As shown the fuse element 23 extendspast the end of the insulation at point 25 and meets and is imbedded ina material 27 sensitive to shock waves. An example of the material 27 islead Styphanate. The shock sensitive material 27 and the end of theinsulated fuse 15 extending through the body 17 is enclosed by a sleeve29 of, for example, brass or thin guilding metal, which is crimped at 31about the fuse train 15 so as to prevent movement thereof through body17. The end of the sleeve 29 is flanged 33 and is enclosed by a nutretainer 35, which is in threaded engagement with the through-hole body17. To ensure a tight fit, Oring seals 37 can be disposed in the body 17adjacent the flanged end 33. The foregoing arrangement thus provides forsecuring the fuse in a fixed relationship outside of the motor case.Additionally the foregoing arrangement provides for securing in a fixedrelationship the fuse to a shock detonating material which willeventually .cause the ultimate detonation of the fuse in rocket motor.

In the initial assembly of the device, a longer than necessary length ofthe insulated pyrotechnic fuse 15 is inserted through the body 17 so theforward case head 13 is moved forward for installation onto the mainmotor case. The insulated fuse 15 is in a slight friction fit withinaperture 18 of the body 17 and is pulled tight from the outside of thehead 13 after the head is installed in the motor case until all slack isremoved. The friction fit holds the fuse in place while trimming the endbefore slipping the flanged sleeve assembly 29 onto the fuse andcrimping it in place. The O-ring seal 37 is inserted in the end of thebody 17 before the uncrimped flanged end 33 of the sleeve assembly isslipped onto the trimmed fuse. The nut retainer ring 35 or othersuitable retaining device is then installed to lock the flanged endsleeve 29 in place.

After the previously described install-ation, the cylindrical housing 39containing the electric detonator and rotor assembly is secured over theexposed fuse ends to the case head 13 by bolts 41. A seal 42 between thehousing and the motor case prevents moisture and the like from enteringthe housing. Mounted on the shell 39 is an electrical connector 43 whichserves to connect pairs of leads 45 and 47 extending therefrom to 'anexternal battery source (not shown). Within the shall 39 the first pairof wires 45 affixed to the connector 43 pass through an electricalpotting insulation 49 made of material such as silicone which serves tohold the wires in place and prevent any movement during the vibration ofthe motor prior to liring. Secured by screws 51 to shell 39 adjacent thepotting composition 49 is an electric detonator assembly 53. Theelectric detonator assembly 53 is comprised of a metal outer shell 55.The electrical potting composition 56 serves to bond the wires 45 inplace as they pass through the shell and insulate the material therein.A wire bridge 57 connects the leads 45 and is imbedded in a compositionknown in the art as the bead 59 which is sensitive and is detonated byheat. An example of such material 59 is lead styphanate. The layeradjacent the bead 59 and within the ceramic enclosure is the sustainingcharge 61 which is of a material that is less sensitive than the beadand can be of boron-potassium nitrate composition.

As can be appreciated, the leads 45 with the bridge 57 therebetween arepermanently affixed to and extend from the electric detonator body andare of sufficient length to pass through the potting composition 49 tothe electrical connector 43. As shown a second pair of leads 47 passthrough the potting composition 49 to a second potting composition 180from the rst described assembly to a second potting composition 63 wherethe leads are connected to a second electrical detonator 65 disposedadjacent the other fuse in the shell. As is apparent, as many electricaldetonators are used in the invention as the number of fuses require,there being one detonator per fuse. Thus, the device is arranged so thatthe electrical detonators are adjacent the crimped end of the fuses.Disposed between the crimped end of the fuse and the electricaldetonator body is a rotor 67 which has a fiat base portion 69 andperpendicular extending side 71 that pass between the electricaldetonator 53 and hanged sleeve assembly 31. An extension 72 of the base69 of the rotor extends through the shell 39 to a rotor arm 73 mountedoutside of the shell. To prevent any leakage of air or atmosphere intothe housing, an O-ring seal 75 can be inserted in the portion of theextension 72 that extends through the shell. As shown in the drawing,the rotor is in the armed position wherein the apertures 76 in the wall71 are aligned with the sleeve assembly 31 and electrical detonator 53.In this particular device, two such apertures would be provided, one foreach fuse 180 apart. The number of apertures would always correspond tothe number of fuses and detonators.

In operation, the rotor 67 is rotated manually by moving arm 73, orelectrically if arm 73 is connected to a suitable means, from a safeposition where there are no through-holes between the anged end sleeveassembly and the electrical detonator to an armed position as shown inth ligure where the through-holes are between the primer end and theelectrical detonator. Upon command an electrical current through theelectrical connector 43 activates an electrical detonator 53. Theactivation is caused by the current passing through the bridge 57warming the material 59 to its ignition point detonating it and in turndetonating the sustaining charge 61.

This causes a significant shock force which passes through the apertures76 in the rotor to the primer material 27 which is sensitive to suchshock force, detonating this material, which in turn detonates fuse end25 carrying such detonation to the main igniter.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

We claim:

1. A safe and arming device for a combustible charge, comprising;

a support structure,

a fuse connected to the support structure,

a detonator positioned in xed relationship with one end of the fuse, thedetonator being separated from said fuse end by a space defining aportion of the detonating path,

a rotor rotatably connected to the support structure,

an annular wall connected to the rotor extending parallel to the axis ofrotation, the wall dening a hollow cavity in which said fuse end isdisposed,

means in the wall forming an opening having an arcuate path of movementintersecting the detonating path,

whereby when the device is in its safe position the opening ismisaligned with the detonating path and when the device is in its armedposition the opening is aligned with the detonating path.

2. The device according to claim 1 wherein;

at least two detonators and two fuses are provided constituting at leasttwo detonating paths,

the support structure is a housing that encloses the detonators and fuseends,

a control is connected to the rotor and extends outside the housing,and,

the wall includes at least two openings that are simultaneously moveableinto alignment with respective detonator paths.

3. The device according to claim 2 wherein;

the fuses are attached to shock sensitive material, and,

the detonators generate shock waves to ignite the fuses when theopenings are aligned with their respective detonating paths.

References Cited UNITED STATES PATENTS SAMUEL FEINBERG, PrimaryExaminer. GERALD H. GLANZMAN, Assistant Examiner,

